1. Field of the Invention
This invention relates to a load for an ultrahigh frequency three-plate straightline with a dielectric substrate.
2. Discussion of the Invention
Ultrahigh frequency energy distribution circuits are, for example, used to feed network antennas. These distribution circuits comprise an input and N outputs, and are generally made in three-plate technology. One of the possible solutions for making these distribution circuits comprises N-1 hybrid rings inserted in meander lines (to make these circuits compact). The uncoupled output of each hybrid ring is connected to a suitable load. When the antenna comprises a large number of radiating elements (elementary antennas), the number N is high, and the distribution circuit therefore comprises a large number of loads. In addition, this distribution circuit is often assembled mechanically, for example by bonding with other circuits of equivalent dimensions, themselves consisting of several superposed layers of dielectric material that is metallized or not.
To be able to reduce the outside dimensions of the distribution circuit, it is necessary, in particular, that the suitable charges themselves be of reduced dimensions, in occupied surface and also in thickness. More precisely, to be able to insert the distribution circuit inside a multilayer structure, it is necessary that the loads be totally integrated into the thickness of the three-plate circuit, because local excess thicknesses are incompatible with an assembly by bonding.
To solve this problem, loads enclosed in metal packages and added to the multilayer structure could be used, which necessitates making local cuts in the three-plate circuit. This solution is incompatible with assembly by bonding of the two dielectric layers of the three-plate circuit. Actually, it necessitates a connection by soldering of the load to the central conductor of the line and an electrical connection by contact of the metal package with the two ground planes of the three-plate.
Another solution would consist in making each load using a series resistor obtained by the etching of a thin resistive film placed between the dielectric material and the metallization of the substrate. A third solution would consist in forming the series resistor by silk screen printing, the resistive material, which appears initially in the form of ink, being polymerized after being deposited on the circuit. For these last two solutions, one end of the series resistor is connected to the ground planes of the three-plate structure with metallized holes. However, these last two solutions are no longer suitable. The second solution can be used only for circuits of reduced dimensions or stiffened with a metal sole because of the fragility of the currently available resistive film, which runs the risk of exhibiting microruptures. The third solution can be used in a three-plate circuit only if the resistive deposit has reproducible characteristics that are stable over time, which is very difficult to attain.